linux-kernel - Re: [PATCH v6 08/26] drm/bridge: panel: add a panel

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Message-ID: <20250210181146.232df79d@booty>
Date: Mon, 10 Feb 2025 18:11:46 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Simona Vetter <simona@...ll.ch>, Inki Dae <inki.dae@...sung.com>, Jagan
 Teki <jagan@...rulasolutions.com>, Marek Szyprowski
 <m.szyprowski@...sung.com>, Catalin Marinas <catalin.marinas@....com>, Will
 Deacon <will@...nel.org>, Shawn Guo <shawnguo@...nel.org>, Sascha Hauer
 <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Daniel Thompson <danielt@...nel.org>,
 Andrzej Hajda <andrzej.hajda@...el.com>, Jonathan Corbet <corbet@....net>,
 Sam Ravnborg <sam@...nborg.org>, Boris Brezillon <bbrezillon@...nel.org>,
 Nicolas Ferre <nicolas.ferre@...rochip.com>, Alexandre Belloni
 <alexandre.belloni@...tlin.com>, Claudiu Beznea <claudiu.beznea@...on.dev>,
 Jessica Zhang <quic_jesszhan@...cinc.com>, Paul Kocialkowski
 <contact@...lk.fr>, Maxime Ripard <mripard@...nel.org>, Neil Armstrong
 <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, Laurent
 Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman
 <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann
 <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Hervé Codina <herve.codina@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, Paul Kocialkowski
 <paul.kocialkowski@...tlin.com>
Subject: Re: [PATCH v6 08/26] drm/bridge: panel: add a panel_bridge to every
 panel

Hi Dmitry,

On Fri, 7 Feb 2025 21:43:26 +0200
Dmitry Baryshkov <dmitry.baryshkov@...aro.org> wrote:

> > > > @@ -1018,6 +1067,11 @@ struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev,
> > > >  {
> > > >  	struct drm_bridge **ptr, *bridge;
> > > >  
> > > > +	if (panel->bridge) {
> > > > +		DRM_DEBUG("panel %s: returning existing bridge=%p", dev_name(dev), panel->bridge);
> > > > +		return panel->bridge;
> > > > +	}    
> > > 
> > > Shouldn't the rest of the function also be removed as you do in other
> > > cases?  
> > 
> > Indeed it should.
> > 
> > And even more, I now realize drm_panel_bridge_add_typed() should also
> > become a simple 'return panel->bridge', like its devm and drmm
> > variants, and its code, implementing the actual creation of a panel
> > bridge, move to an internal function. Otherwise this patch is a bug:
> > existing drivers which do call drm_panel_bridge_add_typed() would end
> > up in having two panel_bridges for the same panel.
> > 
> > I must say the process of developing this patch together with the
> > hotplug work was "convoluted" to say the least, which probably explains
> > why this got unnoticed so far.  
> 
> That's why I suggested to post this series separately - it saves you
> from rebasing hotplug work on top.

Yes, that's sure, but not keeping my hotplug patches on top of the
panel_bridge ones makes it much harder for me to test on real hardware,
so each way has pros and cons.

However I might send only the panel_bridge patches at the next
iteration.

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com